Compulsive behaviors affect about 14% of Parkinson’s patients treated with drugs such as dopamine agonists to ease symptoms like tremors, stiffness, and slowness.

In severe cases, the new addictions that people develop on the drugs can be devastating -- leading to ruined finances and relationships -- and they’ve generated a raft of lawsuits against drug manufacturers.

In November, a French man won a high-profile case against the company that sells Requip, which he said turned him into a sex and gambling addict. In 2008, a Minneapolis man won a case involving gambling addiction against the maker of Mirapex.

As a result, dopamine agonists now carry warnings about compulsive behaviors on their labels.

“A missing piece to the story was whether just Parkinson’s disease itself has any effect or plays any role on the risk of having these problems” without the drugs, says researcher Daniel Weintraub, MD, a psychiatrist at the University of Pennsylvania’s Perelman School of Medicine in Philadelphia.

Tracking Impulsive Symptoms in Parkinson’s Patients

In the largest such study to date, Weintraub and his team set out to answer that question by screening a group of 168 newly diagnosed and untreated people with Parkinson’s for impulsive behaviors. The researchers compared them to a similar group of 143 healthy people who didn’t have the disease.

“What we found was that the reporting of symptoms of impulse control disorders was not any different in the two groups,” Weintraub says.

For example, 1.2% of people with Parkinson’s reported problems related to gambling compared to 0.7% of the healthy group. Compulsive buying behaviors were reported by 3% of the Parkinson’s group compared to 2.1% of the healthy group. About 7% of the Parkinson’s group reported compulsive eating compared to about 11% of the other group. And compulsive sexual behaviors were reported by 4.2% of the Parkinson’s group compared to 3.5% of the healthy group.

Overall, about 20% of both groups showed signs of problems with some kind of impulse control.

The findings, which are in the journal Neurology, are the first published data from the Parkinson’s Progression Markers Initiative, a landmark $50 million effort to follow 400 newly diagnosed patients with Parkinson’s to learn more about how the disease develops. The project is sponsored by the Michael J. Fox Foundation for Parkinson’s Research.

The research echoes the findings of a smaller Italian study, which was published in 2011.

A Complex Interplay Between Drugs and Disease

“To have some confirmation of those findings is important,” says Mark Stacy, MD, a neurologist and professor of medicine at Duke University School of Medicine.

Stacy was one of the first doctors to report problems with impulse control in Parkinson’s patients taking dopamine agonists, but he was not involved in this research. He says the new study suggests that compulsions are probably the result of some complex interplay between the drugs and the disease.

Researchers plan to follow these patients for several years to see if people who show poor impulse control before starting the medications may be more likely than those who don’t to develop impulse control disorders on the drugs.

Doctors have no way to predict which patients will have problems on the drugs.

“Hopefully we can determine if there are specific risk factors for these behaviors going forward,” says Martin Niethammer, MD, PhD, a neurologist at North Shore-LIJ’s Movement Disorders Center in Great Neck, N.Y.

“We now know it’s not part of the disease, so anyone who starts these dopamine agonist medications should be told about these problems,” says Niethammer, who was not involved in the research.